In the most recent update of Seamonkey (2.49.1), I was faced with this notification:

"The Mozilla backend code SeaMonkey is based on, now usually incorporates breaking changes in every release. This is especially true for the Mozilla Gecko add-ons code and the JavaScript interpreter. Consequently, some older extensions may no longer function properly."

FF change of codebase affects Seamonkey. We'll see if Palemoon can stay the course.